1. Field of the Invention
The present invention relates to valves, and more particularly to iris valves used in the control of flow of bulk solids.
2. Description of Related Art
Various valves are used in manufacturing and production facilities to control the flow of materials within the facility, or within systems in the facility. In food handling and other bulk solid material handling fields, for example, valves are used to direct and control the flow of bulk solids to particular machines or particular areas.
Iris valves, employing a flexible sleeve to close the valve opening, are often used in bulk material handling applications since the flexible sleeves cannot damage material passing through the valve. Similarly, the flexible sleeve allows the iris valve to be used in close proximity to bags of bulk material without the danger of damaging the bags.
Current iris valve designs, however, suffer from several drawbacks. For example, for sanitary reasons, all stainless steel construction is preferred in food handling and pharmaceutical handling applications. However, the metal-to-metal contact of the rotating valve parts results in galling of the metal surfaces of the valve, which in turn causes the valve to stick and become difficult to operate. Designs using combinations of bronze and aluminum parts and designs using plastic parts have been introduced to reduce the galling problem, but each suffers from its own drawbacks.
Using bronze and aluminum, alone or in combination, reduces, but does not eliminate, the galling problem. In addition, neither bronze nor aluminum are as strong as stainless steel and do not have the desirable sanitary properties of stainless steel. Rotational parts made of plastic have also been used to avoid the galling problem associated with all-metal construction, however, over time the plastic tends to become brittle and subject to fatigue and breakage.
Thus, there remains a need in the art for an iris valve that incorporates the strength and durability of stainless steel, but is not subject to the galling problems associated with conventional metal-to-metal valve designs.